1982年第11期《数学通报》发表的“三角代换在代数中的应用”一文是从如何进行代换及其应用两方面交织在一起介绍的,比较全面。本文着重谈一下如何进行代换的问题。变量代换法是数学中常用的解题方法,学生比较熟悉。但是,这种代换对于变量来说,是命题中已知条件认可的。即没有改变原变量的允许值范围。否则,会破坏变形的等价性。这一点却往往被学生所忽视。 The article “Application of Triangle Substitution in Algebra” published in the “Mathematical Bulletin,” No. 11 of 1982, was interwoven and described in terms of how to substitute and apply it. This article focuses on how to make substitutions. Variable substitution method is commonly used in mathematics to solve problems, students are more familiar with. However, this substitution is recognized by the known conditions in the proposition for the variable. That is, there is no change in the allowable value range of the original variable. Otherwise, it will destroy the equivalence of deformation. This is often overlooked by students.